| Abstrakt: |
The IESSG, at the University of Nottingham, first initiated studies on the effects of ionospheric scintillation and Total Electron Content (TEC) gradients on GNSS users late in 2000. A network of four state-of-the-art GPS Ionospheric Scintillation Monitor receivers was set up in June 2001 to collect GPS phase and amplitude scintillation parameters, as well as TEC data, forming a Northern European monitoring network. Investigations were then carried out involving in particular the analysis of standalone GPS, DGPS, EGNOS aided DGPS and carrier phase user errors, which have been correlated with observed scintillation levels and with geomagnetic indices. A comprehensive statistical analysis was carried out, aiming to characterise ionospheric scintillation over Northern Europe. Amongst many results from our study, which mostly covered our 2002 data archive, analyses of occurrence of high levels of scintillation disturbing simultaneously a number of satellites showed that, on a day of enhanced geomagnetic activity, for up to nearly 2% of the time, two satellites may be concurrently affected. If it can be shown that scintillation levels over a certain threshold will lead to receiver loss of lock on satellites, then in addition to constellation geometry degradation, this may prove crucial during periods when only 4 or 5 satellites are in view. This scenario, of simultaneous failure of a number of satellites, is the consequential situation most likely to impact on the user community in Northern Europe, especially those involved in safety-critical applications. Also, SBAS (Satellite Based Augmentation Systems) reference stations may be adversely affected during these periods of time as they rely on both GPS carriers (L1 and L2) to compute ionospheric delay corrections for dissemination to users. This paper focuses on our latest results and includes further analyses involving isolated geomagnetically active periods as well as statistical analyses covering a larger part of our data archive (2002–2003), which have recently been carried out aiming to better establish the implications of ionospheric scintillation for GNSS users during the high of the solar cycle. [ABSTRACT FROM AUTHOR] |
